Determining the proper size and fit of alpine ski boots, or the like, made of plastic or relatively rigid, non-conforming material that pivots or flexes only slightly about the ankle axis, can be an uncertain, time consuming process due to the nature of the boot's material and intended use. This process always uses trial and error to arrive at a fit which is comfortable, yet functional.
Two types of boot fitting techniques are currently being used. The first, called boot sizing, involves selecting the proper boot size for a buyer. The second called custom boot fitting, involves modifying the boot's shell or liner to conform to the user's feet. This service is usually requested by users who have tested the boot's fit during alpine skiing and have experienced foot movement inside the boot or localized pain due to the foot's irregularities. The main purpose of custom boot fitting is to obtain greater immobilization of the foot inside the boot for better control of the ski and eliminating foot pain. Both purposes are achieved by adding pads or altering the boot's shell or inner liner as needed. A better form of custom boot fitting is injecting special foam into the boot's liner, that when cured the liner takes the exact shape of the foot.
If the buyer of a pair of boots is not fitted properly and purchases the wrong size, this will soon become apparent when using the boots in their intended use. Consequently, proper boot sizing at purchase is highly desirable.
The typical boot sizing procedure for a buyer is to try on a pair of boots, walk to test for comfort, stand stationary to test the boot's forward flex characteristics by bending the knees forward with as much force as is achievable, roll both ankles left, then right, to apply a side flex on the boot to test the foot's play when making a turn on skis, tighten the buckles, and make other adjustments. This procedure is often repeated, with the boot size changing if it is clearly evident of a wrong size, or changing boot brands if uncomfortable for whatever reason. During custom boot fitting, the above procedure is also used.
The main flaw with these techniques is that the motion of flexing the knees forward and rolling the ankles, which is essential to properly ski alpine style in a controlled and comfortable posture, cannot be sufficiently duplicated because (1) the boot's heel, not being held stationary, lifts during forward flexing, causing the leg to pivot on the toe portion of the boot's sole, instead of about the ankle axis as it does during skiing and (2) there is not enough force restricting the boot from side flexing when a rolling motion of the ankles is applied, causing a poor assessment of how the boot feels when making a turn. Turns are achieved by positioning each ski on its edge, also known as edging the ski.
Another lesser flaw is the walking process. The primary function of the alpine ski boot is to immobilize the foot during skiing, which may not always be comfortable when walking. Walking with alpine ski boots tends to push the foot forward. If, during this process, the toes have sufficient room and are not contacting the inside of the boot, the buyer is deceived into believing the boots must be the correct size and fit because they are comfortable. However, in a properly fitted boot, the toes should make slight contact with the boot when walking, causing a small amount of discomfort. An alpine boot is designed primarily to secure the foot when both the knee and ankle are bent forward, as occurs during the forward flexing action while skiing. The bending at the ankles forces the toes back into the boot's heel whereas walking will cause more joint movement, forcing the toes forward. While more room in the toe section would provide more comfort when walking, it would cause the foot to move excessively during skiing, causing a lesser degree of ski control and possible pain. Therefore, it is important to purchase the proper boot size to fully enjoy the sport. It is in the buyer's best interest to make a purchase decision with emphasis on the primary use of the boot. A means of duplicating the forces caused by leg movement, during skiing, against the boots, would provides a better assessment of the fit than walking and will contribute more toward the purchase decision.
In addition to not being able to sense true foot movement inside the boot with the current fitting technique, the buyer also cannot accurately test the flex characteristics of the boot's material before purchase. Flex characteristics vary with boot design to satisfy the various levels of skiing abilities and it is important to the buyer to purchase a boot that has flex characteristics suitable to their ability. Typically, advanced and high speed skiers use hard flexing boots.
Custom boot fitting service is considered an art by those in the industry, requiring extensive knowledge of the anatomy of the foot, boot design, construction and reaction of the foot inside the boot during skiing or during other activities in the intended use of the boot. With the current fitting techniques, custom boot fitting often involves the trial and error method requiring several visits to assure the best possible fit. Because of the time involved, labor charges are high and therefore any means to reduce this time is desirable.
Custom boot fitting of foam injected boots require the foot to be in the proper skiing postion inside the boot when the foam cures. The proper postion has the foot's heel inside the boot's heel cup with the ankles and knees sightly bent forward. Currently, this is achieved by having the user, wearing the boots, stand unsecured on an inclined platform to elevate the toes. The foam is injected into the liner and the user must remain stationary while the foam cures. Any movement or improper positioning of the foot inside the boot will cause a loose fit. It is therefore also desirable to secure the boots in an elevated position when performing this specialized boot fitting process.